On the Chemical Constituents of the Solar System. 383 



III. The meteoric stones which fall to the earth from inter- 

 planetary spaces show this pre})onderance of the lighter ele- 

 ments still more strikingly. We have the advantage in their 

 case of knowing what is in the interior as well as on the surface, 

 which we do not know of our own globe ; but, on the other hand, 

 we know little or nothing of the atmosphere which, by analogy 

 with the other heavenly bodies, we may suppose to surround 

 each meteoric mass before it mixes with our own air. The 

 various known constituents may be classified as follows : — 



Elements of the Meteorites. 



Plentiful. 



Common. 



Eare. 



Iron. 



Carbon. 



Vanadium 



Magnesium. 



Phosphorus. 



Titanium. 



Calcium. 



Copper. 



Tin. 



Silicon. 



Sodium. 



Potassium 



Oxygen. 



Cobalt. 



Lithium. 



Sulphur. 



Manganese. 



Chlorine. 



Nickel. 



Hydrogen. 





Chromium. 







Aluminium. 







IV. While the above tables give a general result which is 

 unmistakably in accordance with the deductions of theory, 

 there are evident exceptions in detail. Thus bismuth, which 

 has nearly the heaviest of all vapours, is by no means the 

 rarest constituent of the earth ; but then it must also be re- 

 membered that it is one of the most volatile metals, and thus 

 w^ould remain in the atmosphere. On the other hand, gluci- 

 num, with the atomic weight of only 14, is amongst the rare 

 metals ; and lithium, the lightest of all, being only 7, is very 

 small in quantity upon the surface of the earth. Lead, again, 

 with the atomic weight 207, is common. A very natural way 

 of accounting for such exceptions is to suppose that in the 

 original nebula there was but a comparatively small quantity 

 of glucinum and lithium, and a very large quantity of lead ; 

 for of course there is no reason to suppose that the nebulous 

 mass was composed of 60 or 70 elements in equal quantities. 

 There is another circumstance which may be expected to in- 

 terfere with the universality of this rule : compound bodies 

 differ both in volatility and density from the elements from 

 which they are formed, and often without any reference to 

 the mean of their respective quantities. Thus, to take the 

 most familiar instance — water. Oxygen and hydrogen are 

 gases which we have never succeeded in liquefying by any 

 degree of cold or pressure ; but the vapour of their compound 



